Twin-Wall Flue Systems — Components & Cost Guide (UK 2026)
Two-layer insulated stainless steel pipe for installs where there's no masonry chimney. £90–£150/m supply, £180–£250/m installed. Full component reference and supplier list.
What is twin-wall flue?
Twin-wall (also called "system flue" or "insulated flue") is a two-layer stainless steel pipe with insulation between the layers. The outer skin stays cool enough to sit within 50–60mm of combustibles; the inner liner can handle 600°C+ continuous flue temperatures.
Used where there's no existing masonry chimney — for no-chimney installs, garden rooms, conservatories, and modern airtight builds. See our no-chimney install guide for the full installation context.
316 vs 904 — same trade-off as chimney lining
- 316-grade: wood-only use. Standard UK choice for new wood-burning stove installs. Lifespan 10–15 years
- 904-grade: multifuel or smokeless coal use. ~30% more expensive but 50%+ longer lifespan in mixed fuel service. Lifespan 15–25 years
Decision rule: if you might ever burn anything other than wood, go 904. The premium pays for itself in extended service life when burning mineral fuels that produce acidic flue residues.
Twin-wall components and UK 2026 pricing
| Component | Function | Unit price |
|---|---|---|
| 1000mm straight length | Main flue vertical run | £85–£105 |
| 500mm straight length | Structural adjustment piece | £69–£75 |
| Adjustable starter pipe | Direct stove connection (prevents structural strain) | £129–£155 |
| 45-degree elbow | Bypasses joists or exits wall facades | £59 each |
| Wall support bracket | External run structural support every 1.8–2m | £33–£45 |
| Lead roof flashing | Weatherproof seal at pitched roof penetrations | £139 |
| Storm collar | Seals over flashing at roof exit | £35–£50 |
| Anti-downdraft cowl | Terminates flue system; prevents downdrafts | £129–£165 |
Prices for 5" / 6" stainless steel components from UK suppliers. Black powder-coated finish adds ~20% to component costs. Multipliers above apply to base supply pricing.
Typical UK installs — flue length
- Single-storey UK house: 3–5 metres internal
- Two-storey: 5–7 metres internal route, or external up gable wall
- Three-storey or tall Victorian: 7–9 metres total
- Garden room within 2.3m of main house: flue must reach the main house roof height, often pushing total length to 8–12m. See garden room install guide
Black vs stainless finish
Performance-identical. The choice is purely visual:
- Matt black (powder-coated stainless): more popular in modern UK home builds. Adds ~20% to component costs
- Stainless steel: standard appearance, more popular in heritage and traditional installs
Once installed, both develop a slight matte patina from heat cycling. Neither significantly changes appearance over time.
UK twin-wall flue suppliers
- GR8 Fires — broad twin-wall range, online
- Flue Stock — full systems and components
- Stovesonline — Devon, premium ranges
- Flue Direct — UK-wide, free flue design service
- Specflue — trade-focused, large stock
- Stovefitter's Warehouse — DIY kits with guidance
For a complete install, your HETAS-registered installer specifies and sources components. Buying yourself only saves money if you have a HETAS installer who'll fit customer-supplied parts (most prefer specifying themselves for warranty and liability reasons).
Related pages
- No-chimney installation cost guide — full breakdown of twin-wall installation pricing
- Chimney lining guide — the alternative if you have an existing chimney
- Building Regs Part J reference — flue height and clearance requirements
Frequently asked questions
What is a twin-wall flue?
Twin-wall (also "insulated" or "system") flue is a two-layer stainless steel pipe with insulation between the layers. Used where no masonry chimney exists — runs internally through a building or externally up a gable wall. UK pricing: £90–£150 per metre supply, or £180–£250/m installed.
How much twin-wall flue do I need?
Single-storey UK house: 3–5 metres. Two-storey: 5–7 metres. Three-storey or tall Victorian: 7–9 metres. The 2.3m proximity rule can push these substantially higher if you're close to the main house. See our /cost/no-chimney guide for the full breakdown.
316 vs 904 stainless — which grade?
Same trade-off as chimney lining. 316 for wood-only use. 904 for multifuel or smokeless coal — 30% more expensive but 50%+ longer lifespan. Most UK installers default to 316 for new installs unless multifuel is specified.
Black vs stainless finish?
Black powder-coated (matt black) twin-wall costs about 20% more than standard stainless. Visual preference only; both have identical thermal performance. Black is more popular in modern UK home builds; stainless in heritage and traditional installs.
Where can I buy twin-wall flue components?
GR8 Fires, Flue Stock, Stovesonline, Flue Direct, and Specflue are major UK twin-wall suppliers. For a complete install, your HETAS-registered installer specifies and sources components — buying yourself only saves money if you have a HETAS installer agreeing to install supplied parts.